The present invention relates generally to single-use lancets for drawing capillary blood samples. In particular, the present invention provides a single-use lancet which for safety reasons is not capable of being used more than once. Reuse is prevented by a unique trigger mechanism which in the preferred embodiment is irrevocably broken upon firing. The dire consequences of reuse, such as the spread of hepatitis or HIV, are thereby avoided. Furthermore, the present invention is designed so that it may be assembled by automatic machinery. Automatic assembly reduces the cost of the device and assures the highest quality finished product.
Reliable attachment of the main spring to the rear end of the lancet and to the inner body of the device to cause “bounceback” after firing is a pervasive problem in prior art devices. If the spring becomes loose at either end, the lancet will fail to properly retract after firing. The present invention obviates this problem by using a “free floating” spring that does not require any attachments to either end of the lancet. Assembly is simplified and lancet bounceback after firing is reliably accomplished by utilizing plastic spring arms integrally molded into the lancet carrier.
A novel detachable tailpiece on the lancet carrier facilitates automatic or manual assembly. The tailpiece serves as a guide for dropping the spring onto the carrier and helps to stabilize the spring while it is being compressed. The method of spring assembly and cocking of the present invention reduces assembly cost and facilitates quality control.
The needle of single-use devices is driven into the patient's skin by a small spring, which is typically cocked by the technician just prior to use. The safety cap with its attachment keeps the end of the lancet sterile and, since it can be used as a kind of push rod, it is also employed by the user to cock the device. When pulled off, the needle is exposed and the device, having been cocked, is ready for use. Such a device is described in U.S. Pat. No. 5,487,748 to Marshall assigned to Owen Mumford.
One disadvantage of the Marshall device is the ease with which it can be recocked after use. The needle cap can simply be replaced over the end of the lancet and pushed inward to once again cock the spring of the lancet. A small metal rod such as a paperclip can also be used to recock the device described in '748. While such an action is unlikely by a professional blood drawer, it is nevertheless an undesirable feature of a lancet constructed in this fashion.
In an attempt to prevent recocking, another Owen Mumford patent W00243591 describes a single-use device in which the needle carrier has integrally formed spring arms extending rearwardly and alongside the lancet so that after firing, these arms will catch on abutments within the barrel of the device if recocking is attempted by the user. A disadvantage of this technique is that, if the lancet is pulled outward momentarily before being cocked by the user, the spring arms catch on the abutments and the device can therefore not be cocked.
Another method of preventing reuse of the device is described in U.S. Pat. No. 6,168,606 assigned to Palco Labs. In this device, a thin plastic fiber attached between the pull tab and the needle safety cap prevents any compressive force from being applied to the drive spring after firing which effectively prevents recocking of the device. The device must be cocked during manufacturing and is meant to be used after pulling off the finger tab which exposes the needle. A disadvantage of the '606 device is that a small bare area of the needle must remain exposed which could possibly result in airborne contamination since the device is not hermetically sealed.